Large dams vary considerably in their adverse climate impact. From a climate standpoint, there are good dams and bad dams. While some large dams are relatively benign, others ap- pear to release substantial amount of greenhouse gases (GHGs) to the atmosphere. The pres- ence of hydropower dams in the exclusive club of green energy sources must hence be taken up to consideration. The severity of the climate impacts from a hydroelectric project seems to be largely determined by the dam site. While dams at good sites can be very defensible from a climate standpoint, those proposed at bad sites can inherently be highly problematic. This paper provides a simple, yet robust, methodology for comparing proposed hydroelectric project sites in terms of their negative climate impacts. This was done through a thorough literature study, with offset in the UN concept of Land Use, Land-Use Change and Forestry (LULUCF). The concept is defined by the United Nations Framework Convention on Climate Change (UNFCCC) as a “gas inventory sector that covers emissions and removals of greenhouse gases resulting from direct human-induced land use, land-use change and forestry activities”. The findings of the literature study provided the foundation to discuss which variables contribut- ed the most to changes in greenhouse gas budgets for hydroelectric energy production, and in combination with a 2 month fieldtrip to Cambodia, these findings also facilitated a calcula- tion of the approximate cumulative greenhouse impact of the proposed Sambor Hydropower Dam Reservoir in Cambodia. The fieldtrip additionally complimented the study by drawing attention to how local factors can play a significant role in GHG budgets. The variables, which seemed to affect the GWP of hydropower dams the most, appeared to be the total flooded area (including indirectly implicated lands) and the depth of the reservoir. Addition- ally there seems to be a tendency where land-use changes are more significant in the tropical region than elsewhere, and hence that hydropower development in the warmer climates bears with it a much higher degree of risk, with regard to their climate impact - if appropriate considerations are not carefully planned for. With reservation to the many uncertainties coupled with these kinds of budgets, the total re- lease of GHGs in carbon dioxide equivalents from the proposed Sambor Dam reservoir was estimated to be between 153.17 and 204.41 Mt over a 100 year timeframe, or to have a CO2 to energy ratio of 205 to 274 tCO2 pr. GWh, which is substantially higher than other alternative energy solutions, but, also, substantially lower than thermal alternatives.